More than 20,000 people could crowd the Inner Harbor Thursday evening for an NFL season kickoff concert as tens of thousands more flood in for an Orioles game, posing a challenge for transportation workers and police.

The NFL scheduled country star Keith Urban after conflicts with other events forced the Baltimore Ravens to open the regular season in Denver. As he kicks off his concert, thousands of workers will be leaving the office as fans stream into Oriole Park at Camden Yards. Meanwhile, thousands more local music fans will gather several blocks north in West Mount Vernon Park for a monthly "First Thursdays" concert.

City officials say the confluence of events could draw almost as many people as a football game, again testing downtown roads, parking and security just a week after the Grand Prix of Baltimore.

"You plan bigger than what you expect," said Connor Scott, spokesman for the Baltimore City Office of Emergency Management.

Officials are wary of giving crowd estimates for today's NFL Kickoff concert, scheduled at 7:30 p.m. next to the Maryland Science Center, because of the city's football fervor.

Emergency officials know Ravens football fans can surprise them. February's Super Bowl victory parade drew about 200,000 downtown — far more than expected. But the game will not be telecast on concert stages, and Urban is to conclude just before the opening minutes of the 2013 football season.

"We've heard everything," Scott said. "A big reason why we don't expect the world to show up is you can't watch the game there. The true Ravens fans may not show up. Or they may come and leave early."

Security officials are using 20,000 as a general planning guideline, Scott said.

Even if football fans don't show up in droves, the Grammy-award winning Urban, who tours arenas and amphitheaters, can draw thousands on his own.

"We expect there to be a large turnout and we are preparing for a large turnout," Baltimore police spokesman Sgt. Eric Kowalczyk said. "We're treating this as any large-scale event."

Police will deploy waves of officers on foot patrol in the Inner Harbor and put more eyes in the CitiWatch center trained on downtown surveillance cameras. Because Urban will be floating on a 60- by 40-foot concert stage in the harbor, the Coast Guard will limit commercial and recreational boat traffic from 5 p.m. until midnight.

The restricted zone includes all waters from the Baltimore National Aquarium east to the Rusty Scupper restaurant, Coast Guard Petty Officer Jonathan Lindberg said. Vessels berthed, moored or anchored by 5 p.m. will not be forced out of the zone, but none may enter without special permission from port officials.

Grand Prix organizers said they plan to make room for concert-goers by removing one-third of the 39,000 feet of fencing used for the race before the kickoff. City officials said Wednesday that the tear-down was on schedule.

The NFL will have private security on hand at the event, league spokeswoman Joanna Hunter said. Fans can expect their bags to be searched and to go through metal detectors.

The league is urging people to enter at the Baltimore Visitor Center on Light Street at Conway Street or off Key Highway between the Science Center and Rash Field. The event will not close any city streets, the NFL said, and public parking will be available at several downtown garages — though fans are urged to take buses or Light Rail.

The WTMD-sponsored First Thursdays summer concert, which also is free and features multiple bands between 5 p.m. and 8:45 p.m., can draw 5,000 fans or more. The Orioles, who host the Chicago White Sox at 7:05 p.m., have averaged just under 30,000 fans this year at Oriole Park at Camden Yards.

While Ravens fans might have preferred a home game, all the excitement downtown is expected to enliven Baltimore for visitors and local fans.

"Sure, we would've loved to have been here," NFL Commissioner Roger Goodell said Wednesday as he visited the Baltimore headquarters of sports apparel maker Under Armour. "We've made a tradition of that. We also understand. We had a scheduling conflict, and we had to honor that. … But we're going to have a great celebration nonetheless."

The celebration will showcase the city to a national audience as simulcast coverage of a 60-minute pregame show will air from the Inner Harbor on the NBC and NFL networks, league officials said.

"I think it's a wonderful consolation prize for Baltimore," said Kirby Fowler, president of the Downtown Partnership, a business group. "It's always a plus to get free publicity for the city thanks to the NFL, and we think it'll draw lots of attention to the city."

Craig Solomon, a finance worker at Laureate International Universities in Harbor East, came to the Inner Harbor for lunch Wednesday to see all the "hoopla" already under way.

Former Ravens center Mike Flynn and retired St. Louis Rams offensive tackle Orlando Pace signed autographs under a tent while people jumped in a foam-filled pool or played Xbox 360 in a sponsored tent.

With an order of shrimp Pad Thai in one arm and purple beads and a Ravens poster in the other, Solomon said the NFL festivities provided some solace to Ravens fans disappointed that the champs aren't playing their first regular season game at home.

"They're bringing a lot of people into the city with the concert and Keith Urban so they're already kind of making up for it," he said. "It's a pretty good consolation prize. He's an award-winning singer if you like country but it doesn't replace them hosting the game."

Baltimore doesn't get to host the NFL Kickoff game on Thursday night, but fans can still have plenty of fun. There's the Keith Urban concert at 7:30 p.m. And a whole bunch of waterfront restaurants are running food and drink specials for game-watchers.

The Waterfront Partnership said Monday it is looking for firms to create a new design for a $3 million renovation of Rash Field that includes volleyball courts, an event area, and space for exercise and other activities, such as bocce.

As police investigate how a handgun was smuggled into the holding cell of a police station this week, newly released documents show that a man who committed suicide in another police station last year not only had a gun but also a lighter, knife and more than $1,000 in cash.